Resonator sensor assembly

ABSTRACT

An improved method and assembly, wherein the method generally includes the steps of providing a coated or uncoated sensor element having an exposed sensing surface; attaching the sensor element to a platform so that the exposed sensing surface is spaced from the platform; and optionally applying a protective layer over the platform while maintaining the sensing surface as exposed. The assembly includes a resonator having a free portion with a sensing surface is incorporated onto a platform, components of the sensor are physically shielded from harsh operating conditions, the requisite space is maintained between the free portion of the resonator and the platform, and the sensing surface of the resonator remains exposed for sensing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 10/550,075 entitled RESONATOR SENSOR ASSEMBLY, whichapplication is a U.S. national stage of International Application No.PCT/US04/08552, filed Mar. 19, 2004, which application further claimsthe benefit of U.S. Provisional Application No. 60/456,517 entitledRESONATOR SENSOR ASSEMBLY, filed on Mar. 21, 2003, the entire contentsof all of which are herein incorporated by reference for all purposes.

TECHNICAL FIELD

The present invention relates generally to the assembly of sensingdevices, and more particularly to the packaging of fluid conditionsensors such as for the sensing of synthetic or natural petroleumfluids.

BACKGROUND

U.S. Provisional Application No. 60/419,404, (entitled “Machine FluidSensor and Method”; filed Oct. 18, 2002) (hereby incorporated byreference) discloses improved machine fluid sensors and methods. Thereis a need for the ability to package sensing devices so that they canwithstand their operating conditions. Exemplary applications in whichthese sensors may be used in engines in general, automobiles, heavymachinery, military equipment, airplane parts, oil drilling, explorationand production well logging, oil refining, pipeline and quality controlapplications, marine transportation, sub-sea exploration and aerospacerelated equipment, or any other fluid containing application. Ingeneral, sensors for these applications will include very smallcomponents that need to be able to withstand harsh operating environmentconditions. The ability to assemble such devices efficiently usingautomated materials handling equipment is also important.

SUMMARY OF THE INVENTION

In general, the present invention meets the above needs by providing animproved method that generally includes the steps of:

providing a coated or uncoated sensor element having an exposed sensingsurface;

attaching the sensor element to a platform so that the exposed sensingsurface is spaced from the platform; and

optionally applying a protective layer over the platform and/or sensorwhile maintaining the exposed sensing surface.

A highly preferred sensor of the present invention includes a resonator,and more preferably a tuning fork resonator.

Among other advantages, the present invention affords the ability toprovide improved sensor assemblies for a number of differentapplications. The sensor assemblies of the present invention thuspreferably include at least one and more preferably a combination of twoor more of the following:

operates for long periods of time (e.g., at least 3 months, and morepreferably at least 1 year or longer) over a temperature range of −40°C. to 170° C. and more preferably −60° C. to 300° C., without compromiseto the material sensor performance characteristics;

provides protection to fragile components that are typically small(e.g., smaller than 5 mm, and in some instances having a smallestdimension that is smaller than 1 mm), in harsh environments such asenvironments that include corrosive media, abrasive media, orcombinations thereof;

provides a packaged device that is compact (e.g., smaller than about 15cm³, having a footprint of less than about 40 cm², and more preferablysmaller than about 10 cm³, having a footprint of less than about 20cm²), which can be used alone or combined with other components, such asan application specific integrated circuit (ASIC) onto a common platform(e.g., a lead frame or the like);

includes individual or modular components that can be readily handled byautomated materials handling equipment, such as components including aflat surface for handling by “pick and place” robots; or

includes structure that permits for calibration of the sensor against amaterial having a known characteristic or for initializing the sensorupon introduction of a new fluid.

Accordingly, it can be seen that the present invention provides asolution for a number of competing technological challenges; notably,for example, the preparation of an assembly in which a sensor having afree portion with a sensing surface is incorporated onto a platform,components of the sensor are physically shielded from harsh operatingconditions, the requisite space is maintained between the free portionof the sensor and the platform, and the sensing surface of the sensorremains exposed for sensing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side section view of a sensor of the present invention takenfrom the assembly of FIG. 2, wherein the sensor is enveloped by anoptional Faraday cage;

FIG. 2 is a perspective view of the sensor of FIG. 2 with the Faradaycage removed for clarity and depicting an illustrative housingconfiguration;

FIG. 3 a-3 b illustrate (with side sectional views) of a sensor of thepresent invention, shown coupled with another component and sharing acommon platform, and also including an optional protective layer;

FIG. 4 is a top sectional view of an assembly in accordance with thepresent invention to illustrate the use of a removable barrier fortemporary use while applying a protective layer to components of asensor in accordance with the present invention;

FIGS. 5 a-5 d illustrate (with side sectional views) a sequence of stepsemployed for applying a protective layer to components of a sensor inaccordance with the present invention, in which a consumable barrier isemployed;

FIGS. 6 a-6 e illustrate (with side sectional views) a sequence of stepsemployed for assembling another sensor in accordance with the presentinvention;

FIG. 7 illustrates a side view of a sensor of the present inventionattached directly to an ASIC device; and

FIG. 8 a-8 d illustrate (with side sectional views) a sequence of stepsemployed for assembling yet another sensor in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is predicated upon the discovery of methods forassembling a sensor that includes a sensing element that requiresexposure over at least a portion of its outer surface to ambientconditions. More particularly, the present invention is predicated uponthe discovery of methods for assembling a fluid sensor that includes aresonator sensing element that requires exposure over at least a portionof its outer surface to the fluid it is sensing.

One preferred method of the present invention generally includes thesteps of:

providing a coated or uncoated sensor element having an exposed sensingsurface;

attaching the sensor element to a platform so that the exposed sensingsurface is spaced from the platform; and

optionally applying a protective layer over the platform and/or sensorwhile maintaining the exposed sensing surface.

In a particularly preferred embodiment, which is illustrated herein bydescription of a tuning fork resonator as the sensing element, a coatedor uncoated tuning fork resonator is provided and has tines that arefree to resonate upon application of an input signal (e.g., a varyingfrequency input signal). The resonator is attached to a platform in amanner that maintains the tines spaced from the platform. Optionally, aprotective layer is applied over the resonator (other than over thetines) and the platform. It should be appreciated that even though thepresent invention is illustrated with reference to a tuning forkresonator (e.g., having two, three or more tines), the invention is notso limited. For example, the features herein may be employed withrespect to any of a number of types of sensors, including for example,cantilevers, unimorphs, bi-morphs, membrane resonators, torsionalresonators, or other mechanical resonators. The invention may also havesuitable application with respect to thickness shear mode resonators,surface acoustic wave devices, pressure sensing devices, or ultrasonictransducers.

Examples of resonators and the manner of using them for sensingcharacteristics of a fluid are taught, for example, in U.S. Pat. Nos.6,336,353 and 6,182,499, hereby expressly incorporated by reference.

FIG. 1 illustrates one example of an approach to packaging a resonatorto form an assembly 10 in accordance with the present invention. Theassembly 10 includes a resonator 12 having a free portion 14. A baseplatform 16 supports the resonator, by way of a suitable support 18,which may be formed as part of the base platform 16, added as a separatelayer (e.g., a layer of dielectric material (e.g., a polymer, a ceramicor combination thereof), an adhesive such as an epoxy, or the like) orotherwise provided so that the free portion is spaced from the baseplatform over at least a portion of the length of the resonator. Theassembly is preferably provided with a suitable structure adapted forreceiving a signal. For example, in one embodiment, a conductive path 20joins a contact 22 with the resonator (e.g., via a bonded or solderedjoint with an electrode (not shown) associated with the resonator.

The structure of the conductive path and the contact is not critical,and it is possible to combine the two into a single structure. Forexample, it is possible that the conductive path may include a wire thatis attached to an electrode of the resonator. Alternatively, usingtechniques common in the manufacture of semiconductor devices, a via maybe formed in the base platform 16 and filled with a wire or conductivemetal. The contact may be a wire. It may also be a conductive traceapplied by a suitable metallization process (e.g., plating, physicalvapor deposition, chemical vapor deposition, plasma deposition, coating,spraying, or the like). It may also be possible to laminate with orwithout an adhesive.

Though FIG. 1 depicts a structure by which the conductive path extendsthrough a base, it will be appreciated that the invention is not solimited, and the path can extend through or around any wall, e.g., wall24 of the assembly. The wall may be any suitable material, andpreferably is a material similar in electrical characteristics to thematerial of the base platform 16 (e.g., a ceramic, a polymer or acombination thereof).

In FIG. 2, there is shown an example of a more complete housingstructure in which the assembly 10 includes a plurality of walls 24 thatsubstantially surround the resonator. Though shown as generallyorthogonally disposed continuous, flat walls, of course, the inventionis not so limiting, the walls can assume any shape as desired. They mayinclude discontinuities, e.g., grooves, wells, apertures, slits, windowsor some other surface irregularity. The walls may be curved, beconfigured as a polygon other than a rectangle, or combinations thereof.In a preferred embodiment, there is a cut-out defined in the housingstructure so that at least the free portion 14 of the resonator 12 isexposed. For example, as seen in FIG. 2, a top wall may be omitted fromcovering all or a portion of an upper portion of the housing structureto render at least a portion of the resonator exposed to ambient.

In another embodiment, an assembly including a resonator, such as theassembly in FIG. 1 may be combined with one or more other devices, andbe carried together by a common platform. For example, it iscontemplated that a resonator assembly may be packaged in combinationwith an ASIC and be carried by a common platform. With reference to FIG.3 a, there is shown one such example in which an assembly 110, includinga resonator 112 having a free portion 114. A base platform 116 having aconductive path (which in this illustration is shown connected with acontact 122, but need not be, as described above) forms a surface uponwhich a support 118 may be disposed for the resonator 112. A wall 124substantially surrounds the resonator 112, while at least partiallyexposing at least a portion of the resonator to ambient.

Also shown in FIG. 3 a is an additional electronic component 126 (e.g.,an ASIC). Shown in FIG. 3 b is an additional electronic component 126(e.g., an ASIC) and a secondary component 130 (e.g. a temperaturesensor). Furthermore, the one or more devices on the platform may or maynot be surrounded by a wall, which is shown in FIG. 3 a, but absent fromFIG. 3 b.

Secondary components may be included on the common platform with theresonator. Besides temperature sensors (e.g. thermistors, RTDs,semiconductor bandgap or the like), other sensors may be utilized.Beside ASICs, other more general integrated circuits may be used. Also,integrated circuits that combine the functionality several devices orsensors may be used; for example, an integrated circuit that measurestemperature as well operates the resonator may be suitable. A variety ofpassive and/or active components may be used to assist in the operationof the integrated circuit and/or resonator. For example, resistors (e.g.thin film resistors) and capacitors (e.g. ceramic capacitors) may beutilized as passive components. Examples of active components includeamplifiers and/or filters. Also suitable for a use as a secondarycomponent is a field programmable gate array. The conductive path mayalso be considered another device that may be included on the commonplatform with the resonator. In addition, a calibration unit may beutilized. Of course, various combinations of these other devices mayalso be used on a common platform with the resonator.

In a preferred embodiment, the electrical connection between theresonator and the integrated circuit as short as possible to help lessensignal distortions, interferences and parasitic effect that may affectmeasurement accuracy.

In both FIGS. 3 a and 3 b, there is also shown an optional protectivelayer 128 that may be applied to encapsulate at least a portion of theassembly. It will be appreciated that a similar protective layer may beemployed over the various other alternative assemblies of the presentinvention as well, such as over the assembly 10 of FIG. 1. It is notonly limited to the assembly 110 of FIGS. 3 a and 3 b.

The protective layer 128 may be any suitable protective layer. Forexample, it may be a coating that is sprayed, brushed or otherwiseapplied over the assembly; it may also include an overmolded plasticlayer, a layer that is laminated, or combinations of two or more ofcoatings, overmolded layers, or laminated layers may also be employed.

It is found that in instances where it is desired to employ a protectivelayer, and the need remains to maintain the free portion of theresonator exposed to ambient, there is a need to selectively apply theprotective layer to the assembly so that components needing protectionfrom harsh environments will be coated, while still keeping the freeportion of the resonator exposed. Also, the protective layer may beselectively applied to the one or more components on the assembly. Forexample, the protective layer may be selectively applied to thetemperature sensor (item 130 in FIG. 3 b) so that a portion of thetemperature sensor remains exposed to ambient, while the protectivelayer fully coats the additional electronic component. In thealternative, the protective layer may fully coat the temperature sensorif it has a thermal conductivity.

In order to accomplish this, any of a number of suitable selectiveapplication techniques may be employed, such as the employment of aremovable protective barrier to prevent protective layer materials fromcontacting the free portion of the resonator. The removable protectivebarrier is thus positioned over the assembly to block the portions ofthe assembly requiring the protective layer from the portions that donot require the layer. The protective layer is then applied and thebarrier is removed.

The protective barrier may take any suitable configuration, butpreferably is selected from a re-usable barrier or a consumable barrier.For example, it might be possible to employ a photoresist over a portionof the assembly, selectively remove portions thereof, apply theprotective material and then remove remaining photoresist.

FIG. 4 is a top sectional view of a resonator assembly 210 in which are-usable barrier 250 is employed to surround a resonator 212 over afree portion 214, while a protective layer 228 is applied. The re-usablebarrier may be any suitable material. However, preferably it is arelatively soft material that will not plastically deform the resonatorif it contacts the resonator. It may include one or more knife edges252, membranes, walls or the like at any suitable location (e.g., aknife edge seal along an inner periphery) to help sealingly surround theresonator during application of the protective layer. It should beappreciated that though the barrier of this embodiment may be re-usable,it need not be, particularly if to do so would compromise the quality ofthe resulting assembly. The re-usable barrier may be manually handled,or handled by an automated instrument for placement purposes. In avariation within this embodiment, one or a plurality of the barriers maybe placed on a robot arm, which precisely brings the barrier (orbarriers) into proper position relative to the resonator.

FIGS. 5 a-5 d illustrate a sequence of steps that may be employed,pursuant to which the removable protective barrier is a consumablebarrier. In FIG. 5 a there is shown an assembly 310, that includes aresonator 312 having tines defining a free portion 214. The resonatorsits on a platform 318. In FIG. 5 b, a consumable barrier layer 350 isapplied over the resonator of the assembly of FIG. 5 a. In the stepdepicted in FIG. 5 c, a protective layer 328 is applied over theconsumable barrier layer 350. In FIG. 5 d, the consumable layer has beenremoved. Leaving the protective layer 328 in spaced relation from theresonator 312.

In yet another embodiment it may be possible to employ a hybrid approachto the approach of FIGS. 4 and 5 a-5 d. For example, a shell may beformed in situ to surround the resonator. Upon conclusion of applicationof the protective layer, the shell may be removed, such as by breakingit at a weakened region (e.g., a scored location).

It is preferable that any consumable barrier material that is used berelatively inert to the material of the resonator and any associatedhardware so that no damage arises as a result of the method. In thisregard, any of a number of different materials may be employed as theconsumable layer. For example, the material of the consumable barriermay be a material that can be dissolved, decomposed or otherwise brokendown into particles for removal from the volume of space between theresonator and any resulting protective layer. Thus, the consumablebarrier material may be selected from polymers (synthetic, biological,thermoplastic, thermoset, or combinations thereof), starches, waxes,salts or other dissolvable crystals, low melting point metals, oranother sacrificial material that is capable of withstanding in itssolid state the processing conditions for applying the protective layer,and thereafter being removable from the assembly without physicallydeforming or otherwise contaminating the resonator.

Turning now to the embodiment shown in FIGS. 6 a-6 e, there is shownanother approach to the fabrication of an assembly 410 in accordancewith the present invention. In the resulting assembly of thisembodiment, a resonator 412 has a free portion 414 that extends awayfrom a multi-layer holder 460. A first layer 462 is provided as shown inFIG. 6 a. A trench 461 is formed in or on the first layer, as seen inFIG. 6 b, using any suitable material removal or material build-uptechnique (e.g., etching, machining or the like for removal, or plating,physical vapor deposition, chemical vapor deposition, plasma deposition,coating, spraying, laminating with or without adhesive or the like, forbuild-up of spaced walls (not shown) for defining a trench).

According to FIG. 6 c, the resonator 412 is placed in the trench so thatthe free portion projects away from the first layer 462. Though it maybe possible to mechanically fasten the resonator into the trench, or toadhesively bond it in place, FIG. 6 d illustrates the placement of asecond layer 464 over at least a portion of the first layer 462. Thesecond layer may be fabricated on the first layer using any suitabletechnique such as attaching a preformed layer, such as by laminatingwith or without an adhesive, plating, physical vapor deposition,chemical vapor deposition, plasma deposition, coating, spraying, or thelike. At this point the multi-layer holder 460 is complete and may beimplemented into a further assembly. In FIG. 6 e, there is shown oneillustration of how the holder 460 may be incorporated into a furtherassembly, such as by attachment (e.g., via welding, adhesive bonding,wire bonding or the like). In the embodiment of FIG. 6 e, a shielddevice 466 is fabricated to include a protective shield for the freeportion of the resonator, while still maintaining the free portion 414exposed for sensing. Thus, a lower portion 468 is assembled with anupper portion 470 about the resonator 412. Either or both of the lowerportion 468 or the upper portion 470 may include a window that exposesthe free end for sensing. The lower portion 468, the upper portion 470or both may be pre-fabricated to include a suitable cavity 472 forreceiving the resonator. The lower portion 468 and the upper portion 470might also be fabricated separately, or as a single unit (e.g., as amolded plastic clam-shell type package). Though shown in FIG. 6 e asbeing carried by a common platform 418, the holder 460 and shield device466 may be maintained upon separate support surfaces.

FIG. 7 illustrates a side view of an assembly 510 in which a sensor 570including a resonator is attached directly to another device,particularly an ASIC device 572. Though shown mounted on an outersurface 574 of the ASIC device 572, the sensor may penetrate throughsuch an outer surface to an interior of the ASIC device. Attachment ofthe sensor to the ASIC device may be by any suitable technique, such as(without limitation) via welding, adhesive bonding, wire bonding or thelike. The sensor 570 may simply include a resonator, or it may also bean assembly that includes additional packaging, such as that depicted inthe various other embodiments as shown herein (e.g., as in FIGS. 1-6 dand 8 a-8 d).

Turning now to FIGS. 8 a-8 d, there is shown yet another embodiment ofthe present invention in which an assembly 610 includes a first portion680 and a second portion 682 that are attached together in a later-stageassembly step to enclose the assembly while leave a free portion 614 ofresonator 612 exposed for sensing. It should be realized that a suitableshield device, such as shown in FIG. 6 e may likewise be employed withthe present assembly 610. As seen in FIG. 8 a, preferably at least one(or both) of the first or second portions will be configured to includea well 616 for receiving components. Optionally, it may also have asuitable wall structure for defining a opening 618, through or on whichthe resonator 612 may be placed.

In FIG. 8 b a first internal component 620 is placed in the well 616. Inthe step shown in FIG. 8 c, a second internal component 622 (which maybe pre-attached to or otherwise integrated into the first component, oromitted altogether) is placed in the well 616. Optionally, an electricalconductor 624 (e.g., wires, traces or otherwise) is attached to eitheror both of the first or second internal components. Pursuant to FIG. 8d, the resonator is connected with the electrical conductor, the secondportion 682 is secured to the first portion (e.g., mechanically, bywelding, by adhesive bonding or otherwise), and the well is optionallyfilled with an inert substance 684 (e.g., a gas, a gel, a liquid orotherwise).

Thereafter, the resulting assembly can be further handled (e.g., forplacement on a common platform with an ASIC, for placement on an ASIC(as in FIG. 7) or otherwise), such as for attachment to a platform or tohardware for securing it in place in the intended sensing environment.It should be recognized that either of the first or second componentsmight be an ASIC component.

As discussed in the above, in certain embodiments of the presentinvention it is preferable that a spacing be maintained between the freeportion of any resonator and any adjacent structure. The amount of suchspacing is not critical, and may vary depending upon the nature of theparticular application. However, in the context of a preferredembodiment employing a tuning fork resonator, in order to help avoid thepotential for electrical interference with the operation of theresonator, it is preferred that the spacing be at least one width of atine of the tuning fork.

In any of the embodiments discussed herein, it is also possible that oneor more additional structures are added to the assembly in order to helpimprove performance or functionality of the resulting device. Forexample, in one embodiment, the assembly includes a well or othersuitable passage that is in direct fluid communication with theresonator and into which a calibration fluid can be introduced for thepurpose of calibrating the sensor. It is also contemplated that theassembly may include a structure that substantially envelops theresonator for assisting to preserve electrical characteristics. Forexample, a wire mesh 25 or other like cover may be provided about theresonator as a Faraday cage, as illustrated schematically in FIG. 1.Other alternative structures may also be employed, such as themetallization of a region that at least partially surrounds theresonator. This can be employed in any of the above embodiments,including for example the embodiments of FIGS. 1-3 that employ a housingstructure, or the embodiments of FIGS. 6 a-6 e and 8 a-8 d that mightemploy a shield device (which shield device, of course, may also beadapted for employment with a housing such as in FIGS. 1-3).

It should be appreciated that the functions that are described hereinmay be performed as part of a single integrated package, or they may bespread over a plurality of different components that may or may not besupported by a common platform.

Further, the present invention also contemplates the incorporation ofone or more additional sensors apart from the resonator sensorsdescribed herein. For example, one embodiment contemplates the inclusionin an assembly of a sensor or other device for monitoring temperature,such as a thermistor, an RTD or other such temperature sensor (FIG. 3b). In this manner, it is contemplated that all of the data necessaryfor a calculation of viscosity, for example, can be obtained in a singleassembly, which in turn can be interfaced with a suitablemicroprocessor.

It should be recognized that the present invention contemplates not onlythe methods employed for fabricating the assemblies of the presentinvention, but also the assemblies themselves, independent of themethods employed for fabrication. Thus the present inventioncontemplates sensor assemblies that include a resonator having a freeportion with a sensing surface is incorporated onto a platform, whereincomponents of the sensor are physically shielded from harsh operatingconditions, a spacing is maintained between the free portion of theresonator and the platform, and the sensing surface of the resonator isexposed for sensing.

The assemblies of the present invention may also be provided withsuitable hardware for securing the assembly to another component, suchas hardware for securing the assembly in an automotive vehicle engine orwithin a conduit, tank, or other structure for carrying a fluid.

It should also be recognized that even if not described in connectionwith one of the above embodiments, it is possible to combine steps fromone of the embodiments shown with the other embodiments shown. Forexample, for each of the embodiments, it is contemplated that aprotective layer may be applied over at least a portion of the resultingassemblies. This can be done by overmolding, coating or otherart-disclosed techniques for protecting delicate hardware from theeffects of intended operating conditions. Additionally, even if notshown, each of the embodiments might be further assembled onto aplatform alone or with other components using art-disclosed attachmenttechniques (e.g., via welding, adhesive bonding, wire bonding or thelike).

It should also be recognized that single layers shown herein may besplit into additional layers to form more than the number of layersshown, or combined with other layers to form less than the number oflayers shown. All such variations are contemplated within the scope ofthe present invention.

Further, the disclosure herein of a particular shape or orientation of acomponent is not intended as limiting. Though it is expected that manyembodiments will employ relatively thin and flat structures, thecomponents may also be fabricated or arranged so that the resultingstructure has a curvature, a relatively thick profile, or a combinationthereof (e.g., an assembly including a resonator and protective carrierstructure that has a ratio of its largest to its smallest dimension ofabout 1:1 to about 4:1).

Finally, the omission herein in any particular embodiment of anydiscussion of electrical connections or other hardware for signallyconnecting the assemblies herein with other electronic components is notintended as limiting. It should be recognized that a variety ofart-disclosed hardware configurations may be employed in each instance,such as the use of wires, traces, conductive metal filled vias,combinations thereof or the like.

As discussed above, the sensor may be a mechanical resonator, such as isdisclosed for example in U.S. Pat. No. 7,210,332 incorporated byreference herein. The mechanical resonator has a resonator portion forresonating in a fluid and an electrical connection between the resonatorportion and a source of a signal input. The resonator portion, theelectrical connection or both include a base material and aperformance-tuning material. The base material may include quartz,lithium niobate, zinc oxide, lead zirconate titanate (PZT),gallo-germanates (e.g., Langanite (La.₃Ga.₅SiO.₁₄), Langanite, orLangatate), diomignite (lithium tetraborate), bismuth germanium oxidegallium phosphate, gallium nitride, aluminum nitride or combinationsthereof. The performance-tuning material may include polymers, ceramics,metals, metal carbides or nitrides, diamond, diamond-like carbon, andcombinations thereof.

The mechanical resonator may be connected to a measuring system thatsends a variable frequency input signal, such as a sinusoidal wave, thatsweeps over a predetermined frequency range, preferably less than about100 kHz (e.g., in the 25-30 kHz range) for a tuning fork resonator andin a higher range for the TSM resonator. The resonator response over thefrequency range is then monitored to determine selected physical andelectrical properties of the fluid. Absolute values may be obtained ifdesired, as may relative, comparative or index values. Additionally, itis possible also that the system may be employed with determiningwhether a certain threshold criteria is met in the fluid being analyzed.

The hardware for the present measuring system may be any suitablehardware. It may include, for example, art-disclosed network analyzers,see, e.g., U.S. Pat. No. 6,336,353 (Matsiev, et al.) (“Method AndApparatus For Characterizing Materials By Using A MechanicalResonator”); and U.S. Pat. No. 6,182,499 (McFarland, et al.) and U.S.Pat. No. 7,302,830, hereby incorporated by reference. The hardware mightalso be part of an application specific integrated circuit (ASIC), suchas is disclosed for example in U.S. Pat. No. 7,043,969, herebyincorporated by reference, as disclosed in U.S. Pat. No. 6,873,916,hereby incorporated by reference, as disclosed in the applicationentitled “Resonator Sensor Assembly” (published as U.S. Pat. App. No.20040250622 (now abandoned), as disclosed in the application entitled“Environmental Control System Fluid Sensing System And Method”(published International Patent Application No. US03/32983) or asdisclosed in U.S. Pat. No. 7,210,332. All of the foregoing are herebyincorporated by reference.

Generally, the hardware for measuring system provides a versatile fluidsensing system. More specifically, the hardware provides a fluid sensingsystem for machines that rely upon the presence, condition or both of afluid to maintain efficient operation, such as (without limitation) asynthetic or natural engine oil. In an automotive application, the useris provided with the ability to determine the actual condition (e.g. orthe relative deviation of the state of the engine oil from its initialor virgin state) of the engine oil at any particular time, includingduring operation. Alternatively, in conjunction with assessing fluidcondition, the hardware may also determine the amount of fluid remainingin a reserve of an assembly. This advantageously allows machineoperators to extend the duration between fluid service events, whilehelping to assure continued operational integrity of a machine.

Any dynamic assembly that depends on fluids to operate (e.g., wherefriction and heat are of a concern), will benefit from hardware capablesensing the state of a fluid. For instance, the ability to dynamicallymonitor fluid condition, process data obtained from the monitoring, andreport characteristics of the fluid to an interface or operator can havemany applications. Assemblies that may benefit from the definedembodiments of the present invention are many, and can include withoutlimitation, engines in general, automobiles, heavy machinery, militaryequipment, airplane parts, oil drilling, exploration and production welllogging, oil refining, pipeline and quality control applications, marinetransportation, sub-sea exploration and aerospace related equipment, orany other fluid containing application. In addition, contemplatedmethods include a step of assembling the hardware into a device that isincorporated into engines in general, automobiles, heavy machinery,military equipment, airplanes, oil drilling, exploration and productionwell logging equipment, oil refining, pipeline and quality controlequipment, marine transportation equipment, sub-sea exploration andaerospace related equipment, or any other equipment that utilizes fluidsfor operations.

In the automotive field, numerous components require lubrication, whichis not limited to engine oil. For example, other automotive componentsmay include the transmission, the transfer case, the differential, etc.Still further, the sensing system may further be used to determined thequality and amount of other fluids which are not necessarily usedpredominantly as a lubricant, including: brake fluids, steering fluids,antifreeze fluids, refrigerant fluids, windshield washer fluids, or anyother fluid located in an automotive system.

In one embodiment of suitable hardware, an oil sensing system is used todetermine the component characteristics and amount of engine oil. In anautomotive application, the oil sensing system will provide a user, at aminimum, with a warning as to the need to change the oil (such as owingto the presence of contaminants, a breakdown or loss of usefulingredients or otherwise). In such an application, the warning isessentially informing the user of the automobile that the engine oil hasreaches a quality level or condition that is lower than that recommendby the automobile's manufacturer (or set by the oil manufacturer).

The fluid sensing system preferably uses a mechanical resonator as thefluid sensor in accordance with the present invention. The mechanicalresonator is at least partially contained in the fluid under-test. Tomonitor the condition of the fluid under-test (i.e., engine oil), themechanical resonator is provided with electrical energy through afrequency generator. The frequency generator is designed to apply afrequency signal (to the mechanical resonator) that is swept over apredetermined frequency range. Electronics are then used to detect theresponse signal from the mechanical resonator and process the signal toascertain characteristics of the fluid under-test. In an embodiment ofthe fluid sensing system, the electronics are provided in the form of anapplication specific integrated circuit (ASIC). In addition, thehardware might also be part of or include a field programmable gatearray (FPGA).

In the foregoing description, numerous specific details are set forth inorder to provide a thorough understanding of the fluid sensing system,hardware and mechanical resonator that may be used with the presentinvention. It will be apparent, however, to one skilled in the art thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps have notbeen described in detail in order not to unnecessarily obscure thepresent invention.

The manner of operating the resonators and sensors of the presentinvention may vary. In one embodiment, the sensor is operatedcontinuously. In another, it may be intermittently operated. It ispossible that the sensor may be operated only in preselected conditions,such as prior to starting vehicle operation, upon starting vehicleoperation, during vehicle operation upon concluding vehicle operation,while the vehicle travels at a substantially constant velocity, whilethe vehicle accelerates or decelerates, or otherwise.

It should be understood that various alternatives to the embodiments ofthe invention described herein may be employed in practicing theinvention. It is intended that the following claims define the scope ofthe invention and that the methods and apparatus within the scope ofthese claims and their equivalents be covered thereby. To the extentthat the particular combinations of steps and materials covered by thefollowing claims are not disclosed in the specification, thecombinations of steps and materials are incorporated by reference intothe specification.

1. A method of packaging a sensor, the method comprising: affixing atuning fork to a platform, the tuning fork having tines comprising oneor more surfaces, each tine further comprising an electrode; affixing anapplication specific integrated circuit (ASIC) to the platform, andproviding electrical communication between the ASIC and the electrode ofeach tine for providing stimulus to the tuning fork and for receiving aresponse signal from the tuning fork.
 2. The method of claim 1, whereineach tine further comprises a piezoelectric material and wherein theelectrodes are positioned to apply electric fields to the piezoelectricmaterials in the respective tines to move the tines relative to theplatform to displace a fluid in contact with the tines.
 3. The method ofclaim 2, further including applying a protective layer covering theplatform and the tuning fork while maintaining the surface of the tinesuch that the surface can displace the fluid in contact therewith. 4.The method of claim 3, wherein the protective layer is selectivelyapplied by spraying, brushing, over molding, laminating or bycombinations thereof.
 5. The method of claim 4, further includingblocking the surface with a removable protective barrier prior toapplying the protective layer.
 6. The method of claim 5, wherein theremovable protective barrier is a consumable barrier that comprises apolymer, starch, wax, salt or other dissolvable crystal, low meltingpoint metal, a photoresist, or another sacrificial material.
 7. Themethod of claim 5 wherein the removable protective barrier is a reusablebarrier that comprises a relatively soft material that will notplastically deform the tuning fork if it contacts the tuning fork. 8.The method of claim 1, further including affixing a secondary componenton the platform and spaced from the ASIC, the secondary component beingselected from a group consisting of a temperature sensor, a fieldprogrammable gate array, a calibration unit, a conductive path, aresistor, a capacitor, an amplifier, a filter, and combinations of twoor more thereof.
 9. The method of claim 8, further including providingelectrical communication between the ASIC and the secondary component.10. The method of claim 1, further including at least partiallyprotecting the tuning fork from ambient or operational conditionsthrough the use of a housing.
 11. The method of claim 1, furthercomprising operating the tuning fork at temperatures between about −60°C. and about 300° C.
 12. The method of claim 1, wherein the tuning forkhas a length or width smaller than about 5 mm.
 13. The method of claim1, wherein the platform having the tuning fork and the ASIC affixedthereto defines a package, the package having a volume of about lessthan about 15 cm³.
 14. The method of claim 1, wherein the platformhaving the tuning fork and the ASIC affixed thereto defines a package,the package having a footprint of about less than about 40 cm².
 15. Amethod of assembling a fluid sensor, the method comprising: disposing aflexure resonator on a base, the flexure resonator comprising at leasttwo prongs each having an electrode; disposing a control circuit on thebase, and operatively connecting the control circuit to the electrodesfor at least one of transmitting a signal to and receiving a signal fromthe flexure resonator.
 16. The method of claim 15, further includingapplying a protective layer covering the base and the flexure resonator.17. The method of claim 16, further including blocking a portion of theflexure resonator with a removable protective barrier prior to applyingthe protective layer.
 18. The method of claim 15, further includingdisposing a Faraday cage around the flexure resonator.
 19. The method ofclaim 15, further including placing the sensor in one of an engine, atransmission, a transfer case, a differential, a brake system, asteering system, an antifreeze system, a heating and cooling system, awasher system, or combinations thereof.
 20. The method of claim 15,further including placing the sensor in one of a lubricant, a brakefluid, a steering fluid, an antifreeze fluid, a refrigerant fluid, awasher fluid, or combinations thereof.